Late Oligocene to present contractional structure in and around the Susitna basin, Alaska—Geophysical evidence and geological implications

Geosphere
By: , and 

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Abstract

The Cenozoic Susitna basin lies within an enigmatic lowland surrounded by the Central Alaska Range, Western Alaska Range (including the Tordrillo Mountains), and Talkeetna Mountains in south-central Alaska. Some previous interpretations show normal faults as the defining structures of the basin (e.g., Kirschner, 1994). However, analysis of new and existing geophysical data shows predominantly (Late Oligocene to present) thrust and reverse fault geometries in the region, as previously proposed by Hackett (1978). A key example is the Beluga Mountain fault where a 50-mGal gravity gradient, caused by the density transition from the igneous bedrock of Beluga Mountain to the >4-km-thick Cenozoic sedimentary section of Susitna basin, spans a horizontal distance of ∼40 km and straddles the topographic front. The location and shape of the gravity gradient preclude a normal fault geometry; instead, it is best explained by a southwest-dipping thrust fault, with its leading edge located several kilometers to the northeast of the mountain front, concealed beneath the shallow glacial and fluvial cover deposits. Similar contractional fault relationships are observed for other basin-bounding and regional faults as well. Contractional structures are consistent with a regional shortening strain field inferred from differential offsets on the Denali and Castle Mountain right-lateral strike-slip fault systems.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Late Oligocene to present contractional structure in and around the Susitna basin, Alaska—Geophysical evidence and geological implications
Series title Geosphere
DOI 10.1130/GES01279.1
Volume 12
Issue 5
Year Published 2016
Language English
Publisher Geological Society of America
Contributing office(s) Alaska Science Center Geology Minerals
Description 13 p.
First page 1378
Last page 1390
Country United States
State Alaska